Prostheses Joints

The materials used in a total joint replacement ate designed to enable the joint to function normally. The artificial components ate generally composed of a metal piece that fits closely into bone tissue. The metals ate varied and include stainless steel or alloys of cobalt, chrome, and titanium. The plastic material used in implants is a polyethylene that is extremely durable and wear-resistant. Also, a bone cement, a methacrylate, is often used to anchor the artificial joint materials into the bone. Cementiess joint replacements have mote tecentiy been developed. In these replacements, the prosthesis and the bone ate made to fit together without the need for bone cement. The implants ate press-fit into the bone. 

The principal complication for total joint replacement is infection, which may occur just in the area of the incision or more seriously deep around the prosthesis. Infections in the wound area, which may even occur years after the procedure has been performed, are usually treated with antibiotics (qv). 

Nerves are rarely damaged during the total joint replacement surgery. However, nerve damage can occur if considerable joint deformity must be corrected in order to implant the prosthesis. With time these nerves sometimes return to normal function. 

Biomaterials. Just as stem designs have evolved in an effort to develop an optimal combination of specifications, so have the types of metals and alloys employed in the constmction of total joint implants. Pure metals are usually too soft to be used in prosthesis. Therefore, alloys which exhibit improved characteristics of fatigue strength, tensile strength, ductihty, modulus of elasticity, hardness, resistance to corrosion, and biocompatibiUty are used. 

Endoprosthesis A permanent prosthesis used wholly within the body, e.g. as a replacement for a bone, a joint, a tendon or a ligament. 

In a typical hip replacement operation, the top of the thigh bone is removed and a cavity is drilled along the direction of the long axis of the remaining bone. A metal prosthesis is placed in this cavity and secured in place with PMMA cement. In the pelvic girdle a plastic cup is fitted to act as the seat of the new, smaller hip joint. This cup is made of ultra-high molar mass poly (ethylene) and is also secured in place with PMMA cement. The components of an artificial hip joint are shown in Figure 10.1. 

These include attempts by surgeon M.N. Smith-Petersen in 1925, Robert and Jean Judet in 1938, and Dr. Edward J. Haboush in 1953. However, the first successful hip prosthesis was not developed until 1961 when Dr. Chamley made a hip prosthesis out of a high molecular weight polyethylene cup. Today, artificial hip joints are implanted in over 200,000 people each year in the USA (Ratner, 2004). 

Siloxane-containing devices have also been used as contact lenses, tracheostomy vents, tracheal stents, antireflux cuffs, extracorporeal dialysis, ureteral stents, tibial cups, synovial fluids, toe joints, testes penile prosthesis, gluteal pads, hip implants, pacemakers, intra-aortic balloon pumps, heart valves, eustachian tubes, wrist joints, ear frames, finger joints, and in the construction of brain membranes. Almost all the siloxane polymers are based on various polydimethylsiloxanes. 

Thus the only, but extremely widespread, application of zirconium oxide is in the head of the hip joint prosthesis. 

A significant contribution of Raman spectroscopy to the analytical characterization of biomedical issues has been made in the area of biomaterials, especially in the identification of biodegradation and deterioration [1, 2]. The general impact of Raman spectroscopy on the study of biomaterials has been described by this author in three recent review articles [3-5]. In this chapter, the topic of Raman characterization of biomaterials is revisited with particular emphasis placed on those biomaterials widely employed for load-bearing surfaces in artificial joints. Important recent case studies are presented to illustrate the power of the Raman technique to answer key questions of broad medical, scientific, and technological interest. The analytical and physical science lying behind the Raman effect is shown to contribute to the accumulation of a wealth of fundamental information about the medical and technical achievements of prosthesis makers. 

A patient with degenerative joint disease is to undergo insertion of a hip prosthesis. In order to avoid complications due to post-operative infection, the surgeon will pretreat this patient with an antibiotic. This hospital has a significant problem with methicillin-resistant Staphylococcus aureus. Which of the following antibiotics should the surgeon select ... 

The acrylic bone cements have been widely used to successful prosthesis in total joint replacements for the last few decades. While the surgical replacement is very successful, the bone cement is often found as a failed material after long-term use. 

Orthopaedic prosthesis Mechanism of wear of Ultra-high molecular weight polyethylene currently used in total hip and knee joint implants— see J. Mater. Set. 28 1045-1058 (1993). 

Methylmethacrylate is essentially an immunologicaUy inert implant material, but it induces an inflammatory mononuclear cell migration (13,14). Both cemented and cementless prostheses cause a foreign-body-type host response. A new connective tissne capsule is formed around the artificial joint, which is coarser than normal. The reaction is partly granulomatous, with a tendency to necrosis and loosening of the prosthesis. After an initial necrotic phase of 2-3 weeks repair follows, leading to stabilization within 2 years. 

Saint-Maurice C, Migne J, Maurin JP, Vedrine Y, Raud J, Lamas JP. Accidents consecutifs au scellement des protheses articulaires. [Complications following cementing of joint prosthesis.) Ann Anesthesiol Fr 1977 18(7-8) 647-54. 

The application of polymeric materials in medicine is a fairly specialized area with a wide range of specific applications and requirements. Although the total volume of polymers used in this application may be small compared to the annual production of polyethylene, for example, the total amount of money spent annually on prosthetic and biomedical devices exceeds 16 billion in the United States alone. These applications include over a million dentures, nearly a half billion dental fillings, about six million contact lenses, over a million replacement joints (hip, knee, finger, etc.), about a half million plastic surgery operations (breast prosthesis, facial reconstruction, etc.), over 25,000 heart valves, and 60,000 pacemaker implantations. In addition, over AO,000 patients are on hemodialysis units (artificial kidney) on a regular basis, and over 90,000 coronary bypass operations (often using synthetic polymers) are performed each year (]J. 

Joint Replacement. Frequently the joints in the human body must be replaced because of disease or injury. Hundreds of designs have been used in attempts to replace the wide variety of joints with plastics, ceramics, and metals in many combinations. Most of these attempts have had only limited success, but many joints can now be replaced with a reasonably satisfactory prosthesis and thereby restore much of the normal joint function. Essentially all of the most successful replacement joints use a polymeric material. 

As noted earlier, many joint prostheses are held in place by a polymeric cement. This cement is usually a pasty mixture of a methyl methacrylate copolymer and monomeric methyl methacrylate with an added redox initiating system. The paste is pressed into the excavated bone region and polymerized in situ to produce a polymeric mass that then holds the prosthesis by mechanical entrapment. This... 

This High Intelligence Prosthesis for the knee uses an MR fluid damper to provide motion that closely duplicates the naturai movement of the knee joint. 

Most total replacement joints consist of a metallic and a polymeric component, although alternative materials such as ceramics and carbon reinforced materials are currently being examined for this role. The life of a prosthesis is thus directly affected by the rate of penetration of the metallic component into the polymeric component and this has prompted considerable Interest in the subject of wear of polymers in the hostile environment of the body. 

Experiments were carried out in the simulator on an early form of Freeman-Swanson Knee Joint and on a Leeds Knee Joint. Distilled water was allowed to drip onto the prosthesis to wet the interface, the flow rate being adjusted to maintain temperature of the tlbial component at 37 C. Contour diagrams based upon holography are recorded for the initial and worn tlbial components of each joint in Figures 3 and 4 and schematic representations of the wear scars are shown in Figures 5 and 6. 

Figure 4a. Contours of Leeds Knee Prosthesis Tibial Component prior to test in knee joint simulator (Ah = 1.75 /im).

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